1. Field of the Invention
This invention relates to thermal ink jet printing, and more particularly to an improved fabrication process for a thermal ink jet printhead.
2. Description of the Prior Art
Thermal ink jet printing systems use thermal energy to produce a vapor bubble in an ink filled channel to expel an ink droplet on demand. Generally, thermal ink jet printing is accomplished by the use of a printhead comprising one or more ink filled channels which communicate with a relatively small supply chamber at one end and have an opening at the opposite end such as disclosed in U.S. Pat. No. 4,463,359 to Ayata et al. A resistor is located in each of the channels a predetermined distance upstream from the channel orifice. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet.
U.S. Pat. No. 4,601,777 to Hawkins et al discloses a thermal ink jet printhead and method of fabrication. A plurality of printheads are concurrently fabricated by forming a plurality of sets of heating elements with their individual addressing electrodes on one substrate surface and etching corresponding sets of grooves which may serve as ink channels with a common reservoir in the surface of a silicon wafer. The wafer and substrate are aligned and bonded together so that each channel has a heating element. The individual printheads are obtained by milling away the unwanted silicon material in the etched wafer to expose the addressing electrode terminals on the substrate and then the bonded structure is diced into a plurality of separate printheads.
U.S. Pat. No. 4,532,530 to Hawkins discloses a carriage type thermal ink jet printing system having improved bubble generating resistors formed from doped polycrystalline. Glass mesas thermally isolate the active portion of the resistor from the silicon supporting substrate and from the electrode connecting points so that the electrode connection points are maintained relatively cool during operation. A thermally grown dielectric layer permits a thinner electrical isolation layer between the resistor and a protective ink interfacing tantalum layer, thus increasing the thermal energy transfer to the ink.
U.S. Pat. No. 4,571,599 to Rezanka discloses a plurality of disposable individually replaceable ink supply cartridges mountable on the carriage of an ink jet printer. Each cartridge has a thermal ink jet printhead fixedly attached thereto. A constant, slightly negative pressure is maintained at the nozzles of the printhead by means of a secondary reservoir with a level of ink maintained below the ink supply. The majority of the ink is stored in a hermetically sealed main reservoir in the cartridge which contains the ink supply at the negative pressure. A passageway provides ink from the main reservoir to the printhead nozzles. A secondary reservoir within the cartridge holds an air pocket at atmospheric pressure and releases air into the main reservoir as required to maintain the desired negative pressure constant as the ink supply is depleted.
U.S. Pat. No. 4,612,554 to Poleshuk discloses an ink jet printhead composed of substantially two identical parts and method of batch fabricating the parts. Each part has V-grooves anisotropically etched between a linear array of heating elements having selectively addressable electrodes which are parallel to each other. The groove structures of the parts permit them to be mated face to face, so that they may be automatically self-aligned by the intermeshing of the lands containing the heating elements on one part with the grooves of the other part. A pair of parts may be used as a printhead for a carriage-type ink jet printer or a plurality of parts may be assembled for a pagewidth printer.
U.S. Pat. No. 4,639,748 to Drake et al discloses an ink jet printhead having an integral integrated filtering system and fabricating process therefor. Each printhead is composed of two parts aligned and bonded together. One part is substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes. The other part is a flat substrate having a set of concurrently etched recesses in one surface. The set of recesses include a parallel array of elongated recesses for use as capillary filled ink channels having ink droplet emitting nozzles at one end and having interconnection with a common ink supply manifold recess at the other end. The manifold recess contains an internal closed wall defining a chamber with an ink fill hole. Small passageways are formed in the internal chamber walls to permit the passage of the ink therefrom into the manifold. Each of the passageways have smaller cross sectional flow areas than the nozzles to filter the ink, while the total cross sectional flow area of the passageways is larger than the total cross sectional flow area of the nozzles.
U.S. Pat. No. 4,678,529 to Drake et al discloses a method of bonding ink jet printhead components together by coating a flexible substrate with a relatively thin uniform layer of an adhesive having an intermediate non-tacky curing stage with a shelf life around one month for ease of alignment of the parts and ease of storage of the components having the adhesive thereon. About half of the adhesive layer on the flexible substrate is transferred to the high points or lands of the printhead components within a predetermined time of the coating of the flexible substrate by placing it in contact therewith and then peeling it away from the printhead component. The transferred adhesive layer remaining on the printhead component enters an intermediate non-tacky curing stage to assist in subsequent alignment for the printhead components. The printhead components are then aligned and the adhesive layer cured to complete the fabrication of the printhead.
U.S. Pat. No. 4,412,224 to Sugitani discloses a method of forming an ink jet printhead. The ink jet printhead comprises an ink flow path and an ink ejecting nozzle for discharging ink at one end of the ink flow path. The ink flow path is formed by a groove produced at the surface of a substrate by a photoforming technique.
U.S. Pat. No. 4,577,202 to Hara discloses an ink jet printhead for a recording apparatus. A heat generating section is located between at least one pair of confronting electrodes with at least one of the electrodes having a portion lying under an ink storage chamber. The heating generating section comprises a first layer of an inorganic dielectric material, a second layer of an organic material, and a third layer of an inorganic material.
U.S. Pat. No. 4,611,219 to Sugitani et al discloses a thermal ink jet printhead comprising a flat substrate with an array of orifices therein and a base structure on which the flat substrate with the orifices is mounted. The base structure includes a plurality of chambers for receiving the ink and each chamber is exclusively associated with a set of orifices. Each chamber has a number of separate branch paths for conveying the ink to its associated set of orifices in a direction generally parallel to the plane of the flat substrate. Each branch path of the ink has a pressure generating transducer, such as a bubble generating resistor, to eject ink from a corresponding orifice in a direction transverse to the flow direction of the ink in the branch path.
U.S. Pat. No. 4,638,337 to Torpey et al discloses a thermal ink jet printhead having a plurality of capillary filled ink channels each having a droplet emitting nozzle at one end and coupled to an ink supply manifold at the other end. Each channel has a heating element upstream from the nozzle that is located in a recess. The recess walls containing the heating elements prevent the lateral movement of the bubbles through the nozzles and therefore prevent the sudden release of vaporized ink to the atmosphere.
As taught by at least some of the above-mentioned patents, thermal ink jet printheads may be batched produced by placing a plurality of sets of heating elements on one substrate and anisotropically etching plurality of sets of channel grooves and associated manifolds in a second silicon wafer. These were aligned and bonded together and then diced into a plurality of individual printheads. In order to make electrical interconnection to the printhead, such as by wire bonding, to an electrode board commonly referred to as a daughter board, relief grooves had to also be etched in the silicon wafer around each set of ink channels and manifolds, so that when bonded to the heating element substrate, a dicing element could remove the silicon directly above the addressing electrode terminals without contact and damage thereto. The relief groove also prevented contamination of these terminals or contact pads by preventing the application of adhesive thereover during the bonding of the silicon wafer and the heating element substrate.
As discussed later with respect to FIG. 4, flat dicing blades may be used to remove the unwanted silicon material from around the addressing electrode contact pads. However, the anisotropically etched relief grooves, though successful, provide a wafer which relatively fragile before being bonded to the heating element substrate. Thus, the prior art devices encountered a significant problem of channel wafers being broken during handling prior to successful alignment and bonding to the heating element plate.